Fourteen-year-old Marcos Burnett died along with married couple Maria and Will Henniker-Gotley, aged 51 and 55.
The schoolboy was on holiday with his parents and sister who were understood to have been staying in a home owned by the Henniker-Gotleys in Sommati, a village near Amatrice, the when the quake hit.
His parents suffered from minor injuries and are being treated in hospital in Italy.
Mr and Mrs Henniker-Gotley’s two teenage children survived the quake, unhurt it has been reported Both families were from London.
A neighbour, who said she knew the Henniker-Gotleys “very well”, described them as a “lovely family”.
“It’s terrible news, so awful. I knew them all very well, they were very warm and friendly” she said.
Mrs Henniker-Gotley’s father was from the Amatrice region and said the couple had bought the house when he became ill.
Mr Henniker-Gotley was an entrepreneur while his wife worked as a finance director for educational charity Children & The Arts.
Jeremy Newton, chief executive of the charity said: “We are shocked and saddened by the news of her death, and that of her husband Will. We have lost a valued colleague, of course, but, above all, two very dear friends.”
A statement from the Foreign Office confirmed the three deaths and added: “The families have paid tribute to the tireless work of the Italian rescue workers and hospital staff and expressed their gratitude for the love and support they have received from the Italian people.”
The 6.2-magnitude quake hit early on Wednesday morning in a mountainous region 65 miles north-east of Rome.
At least 268 people are now known to have died and 400 have been injured. Rescue teams continue to search the rubble of toppled buildings.
Italy has declared a state of emergency in the regions worst hit and Italian Prime Minister Matteo Renzi has pledged £42m in funds for rebuilding.
Buckingham Palace said the Queen had made a personal donation to support the work of the Italian Red Cross in the search and rescue effort.
Foreign Secretary Boris Johnson said the UK had also offered to help rescuers and additional consular support staff had been deployed to the region.
He added: “My deepest sympathies are with the Italian people and everyone affected by the terrible earthquake that struck central Italy.
Most people were killed were Italian but authorities say five Romanians have died and at least one Spaniard.